Network and fault recovery method

ABSTRACT

A ring network of a multicast label switch path scheme includes a transmitting node and receiving nodes connected to form a ring. A signal input to the transmitting node is branched to be transmitted in first and second different directions to first and second receiving nodes through first and second working paths, respectively, in the ring network. The first and second receiving nodes define terminal points of the first and second working paths, respectively, from the transmitting node. A first backup path is set from the first receiving node to the transmitting node, and a second backup path is set from the second receiving node to the transmitting node. The first backup path is in an opposite direction to the first working path and the second backup path is in an opposite direction to the second working path.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based upon and claims the benefit of priorityof the prior Japanese Patent Application No. 2011-106651 filed on May11, 2011, the entire contents of which are incorporated herein byreference.

FIELD

The embodiments discussed herein are related to a label-switched pathnetwork and a fault recovery method.

BACKGROUND

In recent years, with the advancement of the Ethernet (registeredtrademark) and IP (Internet Protocol) technologies, networks are rapidlybecoming IP-based. This trend has been popular among network providers,so that the SDH (Synchronous Digital Hierarchy) transmission method isstarting to be replaced with the packet transmission method, to addressthe increased demand for IP traffic of carrier networks and to enhancetransmission efficiency for the purpose of reducing cost. The followingdescribes the difference between the SDH transmission method and thepacket transmission method in terms of transmission efficiency.

The SDH method is a technology based on TDM (time-division multiplex),which means time slots may be occupied (used) when there are no data tobe transmitted. On the other hand, in the packet transmission method,when there is no data to be transmitted, the time slots may be used byanother service; therefore the line (use) efficiency is improved.

In a carrier network, from the viewpoint of operational management, evenwhen a packet transmission method is used, path control corresponding tothe SDH method (i.e., static path setting) is to be performed. To meetthis demand, a packet-based transport method called MPLS-TP (MultiProtocol Label Switching-Transport Profile) has been developed.

FIG. 1 indicates an example of a ring network, in which nodes #1 through#8 of the MPLS-TP scheme are connected in a ring shape by links #Athrough #H. FIG. 2 indicates a state where an LSP (Label Switch Path) isset in the network of FIG. 1, extending between node #1 and node #5 vianodes #2 through #4.

A carrier network is demanded to have high availability due to itsnature. Actually, as indicated in FIGS. 3 and 4, there is a working LSPand a backup LSP. In FIG. 3, there is a working LSP in the A direction(clockwise direction) indicated by an arrow of a solid line, and abackup LSP in the B direction (counterclockwise direction) indicated byan arrow of a dashed line. At a receiving node (#5), signals of eitherthe working LSP or the backup LSP are selected. Typically, a receivingnode defining the terminal point is used for monitoring reception of aCCM (Continuity Check Message) packet of OAM (Operation, Administration,and Maintenance), which is a monitor control packet for a working LSPand a backup LSP, to perform fault recovery in units of LSP.

In FIG. 4, there is a ring-shaped working LSP in a clockwise directionindicated by an arrow of a solid line, and a ring-shaped backup LSP in acounterclockwise direction indicated by an arrow of a dashed line. Whena fault occurs, the working LSP is connected to the backup LSP by afault detection node, and fault recovery is performed by bypassing thefault section. In the fault recovery method of FIG. 4, signals do notflow into the backup LSP when a fault has not occurred, and thereforethe line efficiency is higher than that of the fault recovery method ofFIG. 3.

FIGS. 3 and 4 illustrate a fault recovery method of an LSP having apoint to point configuration. However, there is demand for communicationfor performing multicasting to end users in the form of multimediaapplications such as video streaming in a metro network and an internetprotocol television (IPTV). Furthermore, in a cloud service, it isanticipated that demand will increase for 1:N connections, i.e.,multicast communication. There are discussions of standardizing therecovery method of multicast communication at IETF, and various methodsare being proposed (see, for example, non-patent document 1).

Incidentally, the following technology is proposed. There are multipointlogic paths not only for transmitting a frame transmitted from atransmitting terminal node to a multicast frame receiving terminal node,but also for transferring a frame to a transmitting terminal node bycirculating a ring so as to terminate the frame also in the transmissionterminal node. These multipoint logic paths are previously prepared fortwo routes of a working system and a backup system. A node which detectsa fault transmits a forward fault notification frame to the multicastlogic path where the fault has occurred. The transmission terminal nodethat has received the forward fault notification frame stops the use ofthe received multicast logic path and transmits the frame by a pathwhich has not yet received the forward fault notification frame (see,for example, patent document 1).

Furthermore, the following technology is proposed. Along two or morepaths in a network, communication signals are transmitted from ingressnodes to plural egress nodes. There is provided a primary path used fortransmitting multicast communication signals along a communication linkbefore a fault occurs in the network. There is also provided a backuppath for transmitting multicast communication signals along acommunication link. When a fault occurs, multicast communication signalsare transmitted along the primary path at the same time as transmittingcopies of the multicast communication signals along the backup path(see, for example, patent document 2).

Furthermore, the following technology is proposed. The node deviceoperating as a working ring node or a backup ring node on the ringnetwork is provided with a learning part for snooping and learning amessage for performing data relay as data relay information before afault occurs in the working ring node when the node device itselfoperates as a backup ring node, and a working/backup switching part forswitching the node device from a backup ring node to a working ring nodeon the basis of the data relay information learned by the learning partwhen a fault occurs in a working ring node, in the case that the nodedevice is operating as a backup ring node (see, for example, patentdocument 3).

-   Non-patent document 1: draft-liu-mpls-tp-ring-protection-01.txt-   Non-patent document 2:    draft-umansky-mpls-tp-ring-protection-switching-03.txt-   Patent Document 1: Japanese Laid-Open Patent Publication No.    2007-282153-   Patent Document 2: Japanese National Publication of International    Patent Application No. 2010-515314-   Patent Document 3: Japanese Laid-Open Patent Publication No.    2007-228293

FIG. 5 indicates a configuration of an LSP in conventional multicastcommunication. A ring-shaped working LSP in a clockwise directionindicated by an arrow of a solid line is used for delivering packetsfrom a transmitting node #1 to nodes #2, #3, #4, #6, #7, #8.

In a fault recovery method indicated in FIG. 6, when a fault occurs, theworking LSP is connected to the ring-shaped backup LSP in acounterclockwise direction indicated by an arrow of a dashed line, at afault detection node #6. Accordingly, the fault section is bypassed sothat fault recovery is performed. In a fault recovery method indicatedin FIG. 7, a fault at link #F detected by a node #6 and a node #7 isreported to the transmitting node #1, and the signals are bridged toboth the working LSP and the backup LSP at the transmitting node #1, sothat fault recovery is performed.

In the fault recovery methods indicated in FIGS. 6 and 7, it is assumedthat the signals indicated in FIG. 5 are multicast in one direction(clockwise direction) under normal circumstances. Accordingly, undernormal circumstances indicated in FIG. 5, even though the node #8 isadjacent to the transmitting node #1 in terms of the ring topology, thepath circulates the ring, and therefore a large transmission delay iscaused.

Furthermore, when request signals and response signals that aredelivered by multicast from terminals and devices are transferred to theterminals and devices that are the multicast delivery sources, the nodes#8, #7, #6, #4, #3, #2 of FIG. 5 are set as transmitting nodes, and thesignals that are added (inserted) at the respective nodes #8, #7, #6,#4, #3, #2 are transmitted to the node #1 acting as a receiving node. Inthis case also, the path circulates the ring, and therefore a largetransmission delay is caused.

SUMMARY

According to an aspect of the present invention, a ring network of amulticast label switch path scheme, includes a transmitting node and aplurality of receiving nodes connected to form a ring, wherein a signalinput to the transmitting node is branched to be transmitted in firstand second different directions to a first one and a second one of thereceiving nodes through a first working path and a second working path,respectively, in the ring network, the first one and the second one ofthe receiving nodes defining terminal points of the first working pathand the second working path, respectively, from the transmitting node,and a first backup path is set from the first one of the receiving nodesto the transmitting node, and a second backup path is set from thesecond one of the receiving nodes to the transmitting node, wherein thefirst backup path is in an opposite direction to the first working pathand the second backup path is in an opposite direction to the secondworking path.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe appended claims. It is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 indicates an example of a ring network;

FIG. 2 indicates a state where an LSP is set;

FIG. 3 is for describing a working LSP and a backup LSP;

FIG. 4 is for describing a working LSP and a backup LSP;

FIG. 5 indicates a configuration of an LSP in conventional multicastcommunication;

FIG. 6 is for describing a conventional fault recovery method;

FIG. 7 is for describing a conventional fault recovery method;

FIG. 8 illustrates a ring network according to a first embodiment;

FIG. 9 indicates a multicast LSP scheme in the ring network of FIG. 8;

FIG. 10 is a hardware block diagram of a node device according to anembodiment;

FIG. 11 is a functional block diagram of the node device according to anembodiment;

FIG. 12 indicates LSP management information according to a firstembodiment;

FIG. 13 indicates an in-device header according to an embodiment;

FIG. 14 indicates a frame format of an OAM packet;

FIG. 15A is a flowchart of an OAM packet receiving process executed by atransmitting node;

FIG. 15B is a flowchart of an OAM packet transmitting process executedby a transmitting node;

FIG. 16A is a flowchart of an OAM packet receiving process executed by anode defining a terminal point of a working LSP;

FIG. 16B is a flowchart of a switch instruction process executed by anode defining a terminal point of a working LSP;

FIG. 16C is a flowchart of an OAM packet transmitting process executedby a node defining a terminal point of a working LSP;

FIG. 17 is for describing a fault recovery operation;

FIG. 18 is for describing a fault recovery operation;

FIG. 19 is for describing a fault recovery operation;

FIG. 20 is for describing a fault recovery operation;

FIG. 21 is for describing a fault recovery operation;

FIG. 22 illustrates a ring network according to a second embodiment;

FIG. 23 indicates LSP management information according to a secondembodiment;

FIG. 24A is a flowchart of an OAM packet receiving process executed by anode defining a terminal point of a working LSP;

FIG. 24B is a flowchart of a switch instruction process executed by anode defining a terminal point of a working LSP;

FIG. 24C is a flowchart of an OAM packet transmitting process executedby a node defining a terminal point of a working LSP;

FIG. 25A is a flowchart of an OAM packet receiving process in a Cdirection executed by a receiving node;

FIG. 25B is a flowchart of an OAM packet transmitting process in a Cdirection executed by a receiving node;

FIG. 26A is a flowchart of an OAM packet receiving process executed by amiddle node;

FIG. 26B is a flowchart of a switch instruction process executed by amiddle node;

FIG. 26C is a flowchart of an OAM packet transmitting process executedby a middle node;

FIG. 27 is for describing a fault recovery operation;

FIG. 28 is for describing a fault recovery operation;

FIG. 29 is for describing a fault recovery operation;

FIG. 30 is for describing a fault recovery operation; and

FIG. 31 is for describing a fault recovery operation.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will be explained withreference to accompanying drawings.

Configuration of Ring Network First Embodiment

FIG. 8 illustrates a ring network according to a first embodiment. Thering network of FIG. 8 indicates an LSP configuration in multicastcommunication. In FIG. 8, the nodes #1 through #8 of the MPLS-TP schemeare connected in a ring shape by links #A through #H to form a ringnetwork. The ports P1-3, P2-3, P3-3, P4-3, P6-3, P7-3, and P8-3 of therespective nodes are client interface ports for input/output to the ringnetwork. The ports P1-1, P2-1, P3-1, P4-1, P5-1, P6-1, P7-1, and P8-1and the ports P1-2, P2-2, P3-2, P4-2, P5-2, P6-2, P7-2, and P8-2 arenetwork interface ports forming the ring network.

In the ring network of FIG. 8, a multicast LSP indicated in FIG. 9 isformed. In FIG. 9, signals input from the port P1-3 of node #1 arebridged to two working LSPs, namely a working LSP-A in the A direction(clockwise direction) and a working LSP-B in the B direction(counterclockwise direction). A backup LSP-B (nodes #1, #8, #7, #6, #5,#4) in the B direction (counterclockwise direction) is formed as abackup LSP of the working LSP-A (nodes #1, #2, #3, #4) in the Adirection (clockwise direction). That is to say, following the workingLSP-A extending from the transmitting node #1 to the receiving node #4defining the terminal point, there is provided the backup LSP-Bconnecting the receiving node #4 defining the terminal point through thetransmitting node #1 in a ring shape. Among the nodes #1 through #8, atleast the transmitting node or the receiving node defining the terminalpoint of the working LSP has an OAM packet processor (indicated as “OAM”in FIG. 9).

Furthermore, a backup LSP-A (nodes #1, #2, #3, #4, #5, #6) in the Adirection is formed as a backup LSP of the working LSP-B (nodes #1, #8,#7, #6) in the B direction. That is to say, following the working LSP-Bextending from the transmitting node #1 to the receiving node #6defining the terminal point, there is provided the backup LSP-Aconnecting the receiving node #6 defining the terminal point through thetransmitting node #1 in a ring shape.

The node #1 that is a transmitting node has a function of inserting OAMpackets in the working LSP-A in the A direction and the working LSP-B inthe B direction, and a function of receiving OAM packets from the backupLSP-A in the A direction and the backup LSP-B in the B direction.

The OAM packet processor in the node #1 that is a transmitting node hasthe following functions. One function is for periodically transmittingOAM packets of CCM (Continuity Check Message) for connectionconfirmation to the OAM packet processor in the node #4 defining theterminal point that is far away from the transmitting node of theworking LSP-A in the A direction. Another function is for periodicallytransmitting OAM packets of CCM to the OAM packet processor in the node#6 defining the terminal point that is far away from the transmittingnode of the working LSP-B in the B direction. Yet another function isfor transmitting an OAM packet of a switch request (THR-RQ) instructingthe OAM packet processor in the node #6 defining the terminal point ofthe working LSP-B in the B direction to connect the working path to thebackup path, when an OAM packet of a fault report (LOC-F) for reportingthat a fault state has occurred (LOC: Loss of Continuity) is receivedvia the backup LSP-A in the A direction from the OAM packet processor inthe node #4 defining the terminal point of the working LSP-A in the Adirection. Yet another function is for transmitting an OAM packet of aswitch request to the OAM packet processor in the node #4 defining theterminal point of the working LSP-A in the A direction, when an OAMpacket of a LOC fault report is received via the backup LSP in the Bdirection from the OAM packet processor in the node #6 defining theterminal point of the working LSP-B in the B direction.

Furthermore, the receiving nodes #2, 3, and 4 have a function ofdropping (extracting) signals from both the working LSP-A and the backupLSP-B, and the receiving nodes #6, 7, and 8 have a function of droppingsignals from both the working LSP-B and the backup LSP-A.

The node #4 defining the terminal point of the working LSP-A among thereceiving nodes has a function of connecting the working LSP-A to thebackup LSP-A, a function of receiving OAM packets from the working LSP-Aand inserting the received OAM packets in the backup LSP-A, and afunction of connecting from the working LSP-A to the backup LSP-Aaccording to instructions from the OAM packet processor in itself.

The OAM packet processor in the node #4 defining the terminal point ofthe working LSP-A in the A direction has the following functions. Onefunction is for monitoring reception of OAM packets in the workingLSP-A, and detecting a fault state (LOC) when OAM packets are notreceived for a predetermined period. Another function is fortransmitting OAM packets of LOC occurrence reports onto the backup LSP-Ain the A direction to the OAM packet processor in the transmitting node#1, when LOC is detected in the working LSP-A. Yet another function isfor giving an instruction to connect the working LSP-A in the Adirection with the backup LSP-A in the A direction in itself, when anOAM packet of a switching request is received from the OAM packetprocessor in the transmitting node #1 in the working LSP-A.

Among the receiving nodes, the node #6 defining the terminal point ofthe working LSP-B has the following functions. One function is forconnecting from the working LSP-B to the backup LSP-B. Another functionis for receiving an OAM packet from the working LSP-B and inserting theOAM packet in the backup LSP-B. Yet another function is for connectingfrom the working LSP-B to the backup LSP-B, according to the OAM packetprocessor in itself.

The OAM packet processor in the node #6 defining the terminal point ofthe working LSP-B in the B direction has the following functions. Onefunction is for monitoring reception of OAM packets of the workingLSP-B, and detecting a fault state when OAM packets are not received fora predetermined period. Another function is for transmitting OAM packetsof LOC occurrence reports onto the backup LSP-B in the B direction tothe OAM packet processor in the transmitting node #1, when LOC isdetected in the working LSP-B. Yet another function is for giving aninstruction to connect the working LSP-B in the B direction with thebackup LSP-B in the B direction in itself, when an OAM packet of aswitching request is received from the OAM packet processor in thetransmitting node #1 in the working LSP-B.

Hardware Configuration of Node Device

FIG. 10 is a hardware block diagram of a node device according to anembodiment. The node device in FIG. 10 corresponds to the nodes #1through #8 of the MPLS-TP scheme. In FIG. 10, a controller (CONT) 10 isfor setting and controlling the entire device, and includes a CPU 11 andmemories 12 and 13. The memories include a volatile memory (MEM) 12 forprocessing, and a non-volatile memory (NVMEM) 13 for holding setup data.The CPU 11 executes a setting process and a control process by executingprograms read from the memories 12 and 13. A user terminal is connectedto a user interface (UI) 14 when a maintenance person sets the nodedevice.

Furthermore, the memory 13 holds LSP management information used forrouting. The LSP management information includes, for each node, an LSPmanagement number, an input LIU number, an input label, an output 1-LIUnumber, an output 1-label, an output 2-LIU number, and an output2-label.

The CPU 11 of the controller 10 includes interfaces for the respectiveCPUs 21 included in link interface units (LIU) 20, 30, and 40, andreports LSP management information to the link interface units 20, 30,and 40. The controller 10 includes an OAM packet interface function forthe link interface unit 20 and the link interface unit 30, and an OAMpacket processing function, and monitors OAM packets, generates OAMpackets, and gives switching instructions of routing to the linkinterface units.

The link interface units 20 and 30 are for providing network interfaces,and the link interface unit 40 is for providing a client interface. Eachof the link interface units includes a CPU 21, a volatile memory (MEM)22, a physical layer terminal part (PHY) 23, a network processing unit(NPU) 24, and a traffic manager (TM) 25.

The CPU 21 holds LSP management information reported from the controller10 in the volatile memory (MEM) 22, sets the LSP management informationin the NPU 24, and makes settings for policing and shaping of a policer26 and a shaper 27 of the TM 25. Furthermore, the CPU 21 changes therouting by updating the LSP management information of the NPU 24 inaccordance with routing switch instructions from the controller 10.

The physical layer terminal part 23 is a signal interface for networksand client transmission paths. The NPU 24 is a processor and supplementsthe CPU 21.

The receiving side process of the NPU 24 involves checking the LSF #1label value of a received packet, attaching, to the packet, an in-deviceheader including information such as an LSP management number, an inputLIU number, an output 1-LIU number, and an output 2-LIU numbercorresponding to the label value, and transferring the packet to the TM25. Furthermore, in a node including an OAM packet processor, when thelabel value of LSF #2 of the input packet indicates an OAM packet, avalue indicating the controller 10 is set as the output LIU number, andthe signal is transmitted to the TM 25. The transmitting side process ofthe NPU 24 involves removing the in-device header from the transmissionpackets received from the TM 25 and the controller 10, changing the LSF#1 label value to an output label value according to the LSP managementnumber in the in-device header, and transmitting the packets to thephysical layer terminal part 23.

The receiving side process of the TM 25 involves policing a receivedpacket (limiting the rate of the received packet) and transferring thereceived packet to a switch fabric (SWF) 50. When the output LIU numberin the in-device header of the received packet is a value indicating thecontroller 10, the received packet is transferred to the controller 10.The transmitting side process of the TM 25 involves shaping (limitingthe rate of the transmission packet) the packet input from the switchfabric 50, and transferring the transmission packet to the NPU 24.Furthermore, the OAM packet received from the controller 10 istransferred to the NPU 24.

The configuration of the link interface unit 40 is the same as that ofthe link interface units 20 and 30; however, an OAM packet process isnot performed at a client interface, and therefore the link interfaceunit 40 does not have a function of an OAM packet process. The receivingside process of the link interface unit 40 involves attaching an MPLS-TPlabel header and an in-device header to a received packet andtransferring the packet to the TM 25. The transmitting side processinvolves removing the in-device header and the MPLS-TP label header fromthe transmission packet received from the TM 25, and transmitting thepacket to the physical layer terminal part 23.

The switch fabric 50 transfers the packet to the link interface unit(LIU) on the output side, according to the output 1-LIU number/output2-LIU number in the in-device header of the input packet. When LIUnumbers are set in both the output 1-LIU number and the output 2-LIUnumber of the in-device header, the switch fabric 50 creates a copy ofthe input packet and transfers the packets to the link interface unitsindicated by both LIU numbers.

Functional Block Diagram of Node Device

FIG. 11 is a functional block diagram of the node device according to anembodiment. In FIG. 11, a device manager 61 is a functional unit forgenerating user interfaces and LSP management information for devicesettings. The LSP management information that is routing informationcreated by the device manager 61 is stored in a label table storage unit62. The routing information of the label table storage unit 62 issupplied for instructing routing to a label switch processor 63.Furthermore, the routing settings are switched for the label switchprocessor 63 according to instructions from an OAM packet processor 64.

The label switch processor 63 implements routing of signals according torouting information instructed from the label table storage unit 62.Furthermore, if the signals are to be bridged into two directions, thelabel switch processor 63 copies the signals, and then transmits thesignals into the two directions.

The OAM packet processor 64 is supplied with OAM packets extracted atOAM packet extracting units 65 and 66 from reception signals from a portPx-1 (x=1, 2, 3, 4, 5, 6, 7, 8) or a port Px-2, and monitors receptionof OAM packets. Furthermore, the OAM packet processor 64 supplies thegenerated OAM packets to OAM packet insertion units 67 and 68 to insertthe packets in transmission signals, and transmits the transmissionsignals from a port Px-1 or a port Px-2.

The above device manager 61 and the OAM packet processor 64 areimplemented at the controller 10, the label table storage unit 62 isimplemented at the non-volatile memory 13 of the controller 10 and thevolatile memory (MEM) 22 of the link interface units 20 and 30, and thelabel switch processor 63 is implemented at the NPU 24 of the linkinterface units 20 and 30 and the switch fabric 50.

LSP Management Information, in-Device Header, OAM Packet

FIG. 12 indicates LSP management information stored in the label tablestorage unit 62 of each node according to the first embodiment. The LSPmanagement information includes, for each node, an LSP managementnumber, an input LIU number, an input label (LBL), an output 1-LIUnumber, an output 1-label (LBL), an output 2-LIU number, and an output2-label (LBL). These information items are provided for a normal state,a fault state of a working LSP in the A direction, and a fault state ofa working LSP in the B direction. In FIG. 12, the LSP managementinformation items for nodes #1 through #8 are described; however, thelabel table storage unit 62 of each node may only store the LSPmanagement information of its own node.

The information indicates that a signal, which has a label valueindicated by the input LBL of a client interface port or a networkinterface port indicated in the input LIU number, is to be routed as apacket having a label value indicated by an output LBL of a clientinterface port or a network interface port indicated in the output LIU.The information indicates that when there are two output LIUs set forone input, the input signals are to be bridged to two output LIUs. Forexample, at the node #1, a label (LBL)=11 is assigned to an input signalat the port P1-3 and the signal is output from the port P1-1, and alabel (LBL)=21 is assigned to the input signal and the signal is outputfrom the port P1-2.

At the node #4 defining the terminal point of the working LSP, when anOAM packet of a switch request (THR-RQ) is received, the routing of theOAM packet processor 64 is changed to an input LIU number, an inputlabel, an output 1-LIU number, an output 1-label, an output 2-LIUnumber, and an output 2-label of a fault state of the working LSP in theB direction. Accordingly, signals of the working LSP are connected tothe backup LSP. Similarly, at the node #6 defining the terminal point ofthe working LSP, when an OAM packet of a switch request (THR-RQ) isreceived, the routing of the OAM packet processor 64 is changed to aninput LIU number, an input label, an output 1-LIU number, an output1-label, an output 2-LIU number, and an output 2-label of a fault stateof a working LSP in the A direction. Accordingly, signals of the workingLSP are connected to the backup LSP.

FIG. 13 indicates an in-device header according to an embodiment. Thein-device header includes an LSP management number, an input LIU number,an output 1-LUI number, and an output 2-LUI number.

FIG. 14 indicates a frame format of an OAM packet. This frame formatincludes fields of a Destination MAC Address, a Source MAC Address, anda TPID (Type ID), followed by various information fields including LSF#1used for routing, LSF#2 used for distinguishing between signals and OAMpackets, an ACH (Associated Channel Header), and an OAM PDU (PayloadData Unit).

The OAM PDU includes MEL (MEG (Maintenance Entity Group) Level) that isOAM level information, OpCode indicating the type of OAM PDU, Flags usedfor purposes determined according to the type, and TLV offset indicatingthe position of the first TLV in the OAM PDU. When OpCode is 1, it isindicated that the type of the OAM PDU is CCM. OpCodes 52 through 63 arenot used, and for example, OpCode=52 is assigned to a LOC occurrencereport (LOC-F) and OpCode=53 is assigned to a switch request (THR-RQ).Furthermore, for example, OpCode=54 is assigned to a switch request(SW-RQ) described below.

Flowchart

FIGS. 15A and 15B are flowcharts of an OAM packet receiving process andan OAM packet transmitting process in one direction (A direction or Bdirection) executed by the OAM packet processor 64 in the transmittingnode (node #1).

In FIG. 15A, in step S11, N is set in LOC-F_State and a report is sentto the OAM packet transmitting process. In step S12, it is determinedwhether an OAM packet of a LOC occurrence report (LOC-F) has beenreceived, and when LOC-F has been received, the process proceeds to stepS13. In step S13, Y is set in LOC-F_State and a report is sent to theOAM packet transmitting process. In step S14, a LOC-F monitor timer isstarted.

Next, in step S15, the LOC-F monitor timer is incremented, and in stepS16, it is determined whether the LOC-F monitor timer is timed out. Forexample, the LOC-F monitor timer becomes timed out in several tens ofmsec. If the LOC-F monitor timer is not timed out, in step S17, it isdetermined whether an OAM packet of LOC-F has been received.

When LOC-F has been received, in step S18, the LOC-F monitor timer isreset and the process returns to step S15. When LOC-F has not beenreceived, the process returns to step S15 without resetting the timer.Meanwhile, in step S16, when the LOC-F monitor timer is timed out, instep S19, the LOC-F monitor timer is stopped, and the process returns tostep S11.

In FIG. 15B, in step S21, an OAM transmission timer is reset. In stepS22, it is determined whether LOC-F_State=Y. If the determination resultis LOC-F_State=Y in step S22, in step S23, an OAM packet of a switchrequest (THR-RQ) is transmitted. If the determination result isLOC-F_State=N in step S22, in step S24, an OAM packet of CCM formonitoring is transmitted.

Next, in step S25, the OAM transmission timer is incremented, and instep S26, it is determined whether the OAM transmission timer is timedout. The OAM transmission timer becomes timed out in, for example,several msec through several tens of msec. If the OAM transmission timeris not timed out, the process returns to step S25, and if the OAMtransmission timer is timed out, the process returns to step S21.

FIGS. 16A, 16B, and 16C are flowcharts of an OAM packet receivingprocess, a switch instruction process, and an OAM packet transmittingprocess executed by the OAM packet processor 64 in the nodes #4 and #6defining terminal points of the working LSP.

In FIG. 16A, in step S31, N is set in THR-RQ_State and a report is sentto the OAM packet transmitting process. In step S32, N is set inLOC_State and a report is sent to the switch instruction process. Instep S33, the LOC detection timer is started.

Next, in step S34, it is determined whether an OAM packet of CCM orTHR-RQ is received. When an OAM packet of CCM or THR-RQ is not received,in step S35, the LOC detection timer is incremented, and in step S36, itis determined whether the LOC detection timer is timed out. For example,the LOC detection timer becomes timed out in several tens of msec. Ifthe LOC detection timer is not timed out, the process returns to stepS34, and if the LOC detection timer is timed out, the process proceedsto step S37.

In step S37, Y is set in LOC_State and a report is sent to the OAMpacket transmitting process, and N is set in THR-RQ_State and a reportis sent to the switch instruction process. Next, in step S38, it isdetermined whether an OAM packet of CCM or THR-RQ is received. When anOAM packet of CCM or THR-RQ is received, in step S39, it is determinedwhether the OAM packet is of CCM or THR-RQ. When the OAM packet is ofCCM, the process returns to step S32. When the OAM packet is of THR-RQ,in step S40, Y is set in THR-RQ_State and a report is sent to the switchinstruction process, and the process returns to step S32.

Meanwhile, when an OAM packet of CCM or THR-RQ is received at step S34,in step S41, the LOC detection timer is reset. Next, in step S42, it isdetermined whether the OAM packet is of CCM or THR-RQ. When the OAMpacket is of CCM, in step S43, N is set in THR-RQ_State. When the OAMpacket is of THR-RQ, in step S44, Y is set in THR-RQ_State and a reportis sent to the switch instruction process, and the process returns tostep S34.

In FIG. 16B, in step S51, it is determined whether THR-RQ_State=Y. Whenit is determined that THR-RQ_State=Y, in step S52, an instruction isgiven to change routing so that the working LSP is connected to thebackup LSP. When it is determined that THR-RQ_State=N, in step S53, aninstruction is given to change routing so that the working LSP isdisconnected from the backup LSP.

In FIG. 16C, in step S61, the OAM transmission timer is reset. In stepS62, it is determined whether LOC_State=Y. If the determination resultis LOC_State=Y in step S62, in step S63, an OAM packet of a LOCoccurrence report (LOC-F) is transmitted. Next, in step S64, the OAMtransmission timer is incremented, and in step S65, it is determinedwhether the OAM transmission timer is timed out. The OAM transmissiontimer becomes timed out in, for example, several msec through severaltens of msec. If the OAM transmission timer is not timed out, theprocess returns to step S64, and if the OAM transmission timer is timedout, the process returns to step S61.

Description of Fault Recovery Operation

FIG. 17 indicates a normal state. An OAM packet of CCM is transmittedfrom the OAM packet processor 64 in the node #1 onto a working LSP-A inthe A direction and a working LSP-B in the B direction. The OAM packetprocessor 64 in the node #4 defining the terminal point of the workingLSP-A in the A direction and the OAM packet processor 64 in the node #6defining the terminal point of the working LSP-B in the B directionreceive the OAM packet of CCM, and are determined as being in a normalstate.

FIG. 18 indicates a state where a fault has occurred at the link #Gbetween the node #8 and the node #7. Due to a fault in link #G, the OAMpacket processor 64 in the node #6 defining the terminal point of theworking LSP-B in the B direction does not receive an OAM packet of CCMtransmitted by the OAM packet processor 64 in the transmitting node #1.Accordingly, LOC is detected.

Next, as indicated in FIG. 19, the OAM packet processor 64 in the node#6 transmits an OAM packet of a LOC occurrence report (LOC-F) to the OAMpacket processor 64 in the node #1 in the backup LSP-B in the Bdirection.

The OAM packet processor 64 in the node #1 receives an OAM packet ofLOC-F from the node #6 in the backup LSP-B in the B direction.Furthermore, as indicated in FIG. 20, the OAM packet processor 64 in thenode #1 transmits an OAM packet of a switch request (THR-RQ) onto theworking LSP-A in the A direction to the OAM packet processor 64 in thenode #4

The OAM packet processor 64 in the node #4 receives the OAM packet ofTHR-RQ from the node #1 in the working LSP-A in the A direction.Furthermore, as indicated in FIG. 21, the OAM packet processor 64 in thenode #4 gives an instruction to connect the working LSP-A in the Adirection with the backup LSP-A in the A direction in itself.Accordingly, the nodes #1 through #8 perform the switch according todescriptions relevant to a fault occurring in the working LSP in the Bdirection in the LSP management information indicated in FIG. 12.According to the above operations, signals of the working LSP in the Adirection are connected to the backup LSP-A in the A direction in thenode #4, and are transmitted to the node #6 and the node #7 via the node#5, and the fault is recovered. That is to say, the transmission delayunder normal circumstances is reduced. Furthermore, at the time of faultrecovery, the working LSP-A (nodes #1, #2, #3, #4) and the backup LSP-A(nodes #4, #5, #6, #7) in the A direction do not overlap each other, andtherefore the signal band is efficiently used.

The present embodiment is applicable to a working multicast label switchpath and a backup multicast label switch path that are linked, and thenetwork topology is not limited to a ring.

Second Embodiment

FIG. 22 illustrates a ring network according to a second embodiment. Thering network of FIG. 22 indicates an LSP configuration for transferringrequest signals and response signals that are delivered by multicastfrom terminals and devices to the terminals and devices that are themulticast delivery sources.

FIG. 22 indicates an example of a ring network, in which the nodes #1through #8 of the MPLS-TP scheme are connected in a ring shape by links#A through #H.

Furthermore, as a backup LSP for a working LSP-C (nodes #4, #3, #2, #1)in the C direction (counterclockwise direction), a backup LSP-D (nodes#4, #5, #6, #7, #8, #1) in the D direction (clockwise direction) isformed. That is to say, following the working LSP-C extending from thereceiving node #1 to the transmitting node #4 defining the terminalpoint, there is provided the backup LSP-D connecting the transmittingnode #4 defining the terminal point through the receiving node #1 in aring shape.

Furthermore, as a backup LSP for a working LSP-D (nodes #6, #7, #8, #1)in the D direction, a backup LSP-C (nodes #6, #5, #4, #3, #2, #1) in theC direction is formed. That is to say, following the working LSP-Dextending from the receiving node #1 to the transmitting node #6defining the terminal point, there is provided the backup LSP-Cconnecting the transmitting node #6 defining the terminal point throughthe receiving node #1 in a ring shape. Among the nodes #1 through #8, atleast the transmitting node or the receiving node defining the terminalpoint of the working LSP has an OAM packet processor (indicated as “OAM”in FIG. 22).

The receiving node #1 has a function of receiving OAM packets from theworking LSP-C in the C direction and the working LSP-D in the Ddirection, and a function of adding (inserting) OAM packets to thebackup LSP-C in the C direction and the backup LSP-D in the D direction.

The OAM packet processor 64 in the receiving node #1 has the followingfunctions. One function is for monitoring reception of OAM packets inthe working LSP-C in the C direction, and detecting a fault state (LOC)in the C direction when OAM packets are not received for a predeterminedperiod. Another function is for monitoring reception of OAM packets inthe working LSP-D in the D direction, and detecting a fault state (LOC)in the D direction when OAM packets are not received for a predeterminedperiod. Yet another function is for transmitting OAM packets of LOCoccurrence reports (LOC-F) onto the backup LSP-C in the C direction tothe OAM packet processor 64 in the node #4 defining the terminal pointfar away from the receiving node in the working LSP-D in the Ddirection, when LOC is detected in the working LSP-C in the C direction.Yet another function is for transmitting OAM packets of LOC occurrencereports (LOC-F) onto the backup LSP-D in the D direction to the OAMpacket processor 64 in the node #6 defining the terminal point far awayfrom the receiving node in the working LSP-C in the C direction, whenLOC is detected in the working LSP-D in the D direction.

The transmitting nodes #2, #3, #4, #6, #7, #8 have a function ofselecting either one of a working LSP and a backup LSP and adding(inserting) signals.

The transmitting node #4 defining the terminal point of the working LSPin the C direction has the following functions. One function is forconnecting the backup LSP-C to the working LSP-C. Another function isfor inserting OAM packets in the working LSP-C, and receiving OAMpackets from the backup LSP-C. Yet another function is for switching theLSP to which signals are to be added, from the working LSP-C to thebackup LSP-D, according to instructions from the OAM packet processor 64in itself.

The transmitting node #6 defining the terminal point of the working LSPin the D direction has the following functions. One function is forconnecting the backup LSP-D to the working LSP-D. Another function isfor inserting OAM packets in the working LSP-D, and receiving OAMpackets from the backup LSP-D. Yet another function is for switching theLSP to which signals are to be added, from the working LSP-D to thebackup LSP-C, according to instructions from the OAM packet processor 64in itself.

The OAM packet processor 64 in the transmitting node #4 defining theterminal point of the working LSP-C in the C direction has the followingfunctions. One function is for periodically transmitting OAM packets ofCCM onto the working LSP-C in the C direction to the OAM packetprocessor 64 in the receiving node #1. Another function is fortransmitting OAM packets of switch requests (SW-RQ) onto the workingLSP-C in the C direction and switching the LSP to which signals are tobe added from the working LSP-C to the backup LSP-D, when an OAM packetof an LOC occurrence report (LOC-F) is received from the OAM packetprocessor 64 in the receiving node #1 via the backup LSP-C in the Cdirection.

The OAM packet processor 64 in the transmitting node #6 defining theterminal point of the working LSP in the D direction has the followingfunctions. One function is for periodically transmitting OAM packets ofCCM onto the working LSP-D in the D direction to the OAM packetprocessor 64 in the receiving node #1. Another function is fortransmitting OAM packets of switch requests (SW-RQ) onto the workingLSP-D in the D direction and switching the LSP to which signals are tobe added from the working LSP-D to the backup LSP-C, when an OAM packetof an LOC occurrence report (LOC-F) is received from the OAM packetprocessor 64 in the receiving node #1 via the backup LSP-D in the Ddirection.

Among the transmitting nodes, the nodes #2 and #3 in the middle of theworking LSP-C have a function of receiving and relaying the OAM packetsof the working LSP-C, and a function of switching the LSP to whichsignals are to be added from the working LSP-C to the backup LSP-Daccording to instructions from the OAM packet processor 64 inthemselves. Nodes in the middle are the transmitting nodes excludingtransmitting nodes defining the terminal points of the LSP.

Among the transmitting nodes, the nodes #7 and #8 in the middle of theworking LSP-D have a function of receiving and relaying the OAM packetsof the working LSP-D, and a function of switching the LSP to whichsignals are to be added from the working LSP-D to the backup LSP-Caccording to instructions from the OAM packet processor 64 in itself.

The OAM packet processor 64 in the nodes #2 and #3 in the middle of theworking LSP-C has the following functions. One function is for relayingan OAM packet of CCM transmitted by the transmitting node #4 definingthe terminal point of the working LSP-C to the next working LSP-C.Another function is for relaying a received OAM packet to the nextworking LSP-C and switching the LSP to which signals are to be addedfrom the working LSP-C to the backup LSP-D, when an OAM packet of aswitch request (SW-RQ) transmitted by the transmitting node #4 definingthe terminal point of the working LSP-C is received.

The OAM packet processor 64 in the nodes #7 and #8 in the middle of theworking LSP-D has the following functions. One function is for relayingan OAM packet of CCM transmitted by the transmitting node #6 definingthe terminal point of the working LSP-D to the next working LSP-D.Another function is for relaying a received OAM packet to the nextworking LSP-D and switching the LSP to which signals are to be addedfrom the working LSP-D to the backup LSP-C, when an OAM packet of aswitch request (SW-RQ) transmitted by the transmitting node #6 definingthe terminal point of the working LSP-D is received.

The hardware configuration and functional blocks of the node devicesaccording to the second embodiment are the same as those indicated inFIGS. 10 and 11. Furthermore, the in-device header and OAM packets arealso as indicated in FIGS. 13 and 14.

LSP Management Information

FIG. 23 indicates LSP management information stored in the label tablestorage unit 62 of each node according to the second embodiment. The LSPmanagement information includes, for each node, an LSP managementnumber, an input LIU number, an input label (LBL), an output 1-LIUnumber, an output 1-label (LBL), an output 2-LIU number, and an output2-label (LBL). These information items are provided for a normal state,a recovering state of a working LSP in the C direction, and a recoveringstate of a working LSP in the D direction. In FIG. 23, the LSPmanagement information items for nodes #1 through #8 are described;however, the label table storage unit 62 of each node may only store theLSP management information of its own node.

The information indicates that a signal, which has a label valueindicated by the input LBL of a client interface port or a networkinterface port indicated in the input LIU number, is to be routed as apacket having a label value indicated by an output LBL of a clientinterface port or a network interface port indicated in the output LIU.The information indicates that when there are two output LIUs set forone input, the input signals are to be bridged to two output LIUs.

The nodes #4 and #6 defining the terminal points of the working LSPchange the routing of the label switch processor 63 when an OAM packetof a LOC occurrence report (LOC-F) is received. The transmitting nodes#2, #3, #4, #6, #7, #8 change the routing of the label switch processor63 when an OAM packet of a switch request (SW-RQ) to implement signalconnection from a working LSP to a backup LSP is received.

Flowchart

FIGS. 24A, 24B, and 24C are flowcharts of an OAM packet receivingprocess, a switch instruction process, and an OAM packet transmittingprocess executed by the OAM packet processor 64 in the nodes #4 and #6defining terminal points of the working LSP.

In FIG. 24A, in step S101, N is set in LOC-F_State and a report is sentto the OAM packet transmitting process and the switch instructionprocess. In step S102, it is determined whether an OAM packet of a LOCoccurrence report (LOC-F) has been received, and when LOC-F has beenreceived, the process proceeds to step S103. In step S103, Y is set inLOC-F_State and a report is sent to the OAM packet transmitting processand the switch instruction process. In step S104, an LOC-F monitor timeris started.

Next, in step S105, the LOC-F monitor timer is incremented, and in stepS106, it is determined whether the LOC-F monitor timer is timed out. Forexample, the LOC-F monitor timer becomes timed out in several tens ofmsec. If the LOC-F monitor timer is not timed out, in step S107, it isdetermined whether an OAM packet of LOC-F has been received.

When LOC-F has been received, in step S108, the LOC-F monitor timer isreset and the process returns to step S105. When LOC-F has not beenreceived, the process returns to step S105 without resetting the timer.Meanwhile, in step S106, when the LOC-F monitor timer is timed out, instep S109, the LOC-F monitor timer is stopped, and the process returnsto step S101.

In FIG. 24B, in step S111, it is determined whether LOC-F_State=Y. Whenit is determined that LOC-F_State=Y, in step S112, an instruction isgiven to change routing of adding signals to the backup LSP. When it isdetermined that LOC-F_State=N, in step S113, an instruction is given tochange routing of adding signals to the working LSP.

In the FIG. 24C, in step S121, the OAM transmission timer is reset. Instep S122, it is determined whether LOC-F_State=Y. If the determinationresult is LOC-F_State=Y in step S122, in step S123, an OAM packet of aswitch request (SW-RQ) is transmitted. If the determination result isLOC-F_State=N, in step S124, an OAM packet of CCM for monitoring istransmitted.

Next, in step S125, the OAM transmission timer is incremented, and instep S126, it is determined whether the OAM transmission timer is timedout. The OAM transmission timer becomes timed out in, for example,several msec through several tens of msec. If the OAM transmission timeris not timed out, the process returns to step S125, and if the OAMtransmission timer is timed out, the process returns to step S121.

FIGS. 25A and 25B are flowcharts of an OAM packet receiving process inthe C direction and an OAM packet transmitting process in the Cdirection executed by the OAM packet processor 64 in the receiving node#1.

In FIG. 25A, in step S132, N is set in LOC-F_State and a report is sentto the switch instruction process. In step S133, the LOC detection timeris started.

Next, in step S134, it is determined whether an OAM packet of CCM orSW-RQ is received. When an OAM packet of CCM or SW-RQ is not received,in step S135, the LOC detection timer is incremented, and in step S136it is determined whether the LOC detection timer is timed out. Forexample, the LOC detection timer becomes timed out in several tens ofmsec. If the LOC detection timer is not timed out, the process returnsto step S134, and if the LOC detection timer is timed out, the processreturns to step S137.

In step S137, the LOC detection timer is reset. In step S138, Y is setin LOC_State and a report is sent to the OAM packet transmitting processin the C direction. Next, in step S139, it is determined whether an OAMpacket of CCM or SW-RQ has been received. When an OAM packet of CCM orSW-RQ has been received, the process returns to step S132.

Meanwhile, when an OAM packet of CCM or SW-RQ has been received in stepS134, in step S140, the LOC detection timer is reset and the processreturns to step S134.

In FIG. 25B, in step S151, the OAM transmission timer is reset. In stepS152, it is determined whether LOC_State=Y. If the determination resultis LOC_State=Y in step S152, in step S153, an OAM packet of an LOCoccurrence report (LOC-F) is transmitted. Next, in step S154, the OAMtransmission timer is incremented, and in step S155, it is determinedwhether the OAM transmission timer is timed out. The OAM transmissiontimer becomes timed out in, for example, several msec through severaltens of msec. If the OAM transmission timer is not timed out, theprocess returns to step S154, and if the OAM transmission timer is timedout, the process returns to step S151.

The OAM packet processor 64 in the receiving node #1 executes the OAMpacket reception process in the D direction and the OAM packettransmission process in the D direction in the same manner as thoseindicated in FIG. 25A and FIG. 25B.

FIGS. 26A, 26B, and 26C are flowcharts of an OAM packet receivingprocess, a switch instruction process, and an OAM packet transmittingprocess executed by the OAM packet processor 64 in the middle nodes #2,#3, #7, #8.

In FIG. 26A, in step S161, N is set in CCM_FLG and SW-RQ_FLG and areport is sent to the OAM packet transmitting process. In step S162, Nis set in SW-RQ_State and a report is sent to the switch instructionprocess.

Next, in step S163, it is determined whether an OAM packet of CCM orSW-RQ is received. When an OAM packet of CCM or SW-RQ is received, theprocess proceeds to step S164, and it is determined whether the OAMpacket is of CCM or SW-RQ. When the OAM packet is of CCM, in step S165,Y is set in CCM_FLG and a report is sent to the OAM packet receptionprocess, and the process returns to step S163. When the OAM packet is ofSW-RQ, in step S166, Y is set in SW-RQ_FLG and a report is sent to theOAM packet reception process, in step S167, Y is set in SW-RQ_State anda report is set to the switch instruction process, and in step S168, aSW-RQ detection timer is started.

Next, in step S169, it is determined whether an OAM packet of CCM orSW-RQ is received. When an OAM packet of CCM or SW-RQ is not received,in step S170, the SW-RQ detection timer is incremented, and in stepS171, it is determined whether the SW-RQ detection timer is timed out.For example, the SW-RQ detection timer becomes timed out in several tensof msec. If the SW-RQ detection timer is not timed out, the processreturns to step S169, and if the SW-RQ detection timer is timed out, instep S172, the SW-RQ detection timer is reset and the process returns tostep S162.

Next, in step S169, when an OAM packet of CCM or SW-RQ is received, instep S173, it is determined whether the OAM packet is of CCM or SW-RQ.When the OAM packet is of CCM, in step S174, Y is set in CCM_FLG and areport is sent to the OAM packet reception process, and the processproceeds to step S172. When the OAM packet is of SW-RQ, in step S175, Yis set in SW-RQ_FLG and a report is sent to the OAM packet receptionprocess. Next, in step S176, the SW-RQ detection timer is reset and theprocess returns to step S169.

In FIG. 26B, in step S181, it is determined whether SW-RQ_State=Y. Whenit is determined that SW-RQ_State=Y, in step S182, an instruction isgiven to change routing so that the LSP to which signals are added isswitched to the backup LSP. When it is determined that SW-RQ_State=N, instep S183, an instruction is given to change routing so that the LSP towhich signals are added is switched to the working LSP.

In the FIG. 26C, in step S191, the OAM transmission timer is reset. Instep S192, it is determined whether CCM_FLG=Y. If the determinationresult is CCM_FLG=Y in step S192, in step S193, an OAM packet of CCM istransmitted, and in step S194, N is set in CCM_FLG, and the processproceeds to step S195. If the determination result is CCM_FLG=N in stepS192, the process proceeds to step S195.

In step S195, it is determined whether SW-RQ_FLG=Y. If the determinationresult is SW-RQ_FLG=Y in step S195, in step S196, an OAM packet of SW-RQis transmitted, and in step S197, N is set in SW-RQ_FLG, and the processproceeds to step S198.

In step S198, the OAM transmission timer is incremented, and in stepS199, it is determined whether the OAM transmission timer is timed out.The OAM transmission timer becomes timed out in, for example, severalmsec through several tens of msec. If the OAM transmission timer is nottimed out, the process returns to step S198, and if the OAM transmissiontimer is timed out, the process returns to step S191.

Description of Fault Recovery Operation

FIG. 27 indicates a normal state. From the OAM packet processor 64 inthe node #4 defining the terminal point of the working LSP-C, an OAMpacket of CCM is transmitted onto the working LSP-C in the C direction.From the OAM packet processor 64 in the node #6 defining the terminalpoint of the working LSP-D, an OAM packet of CCM is transmitted onto theworking LSP-D in the D direction. The OAM packet processor 64 in thereceiving node #1 receives OAM packets of CCM from the working LSP-C andthe working LSP-D, which are determined as being in a normal state. Alltransmitting nodes transmit signals to the working LSP.

FIG. 28 indicates a state where a fault has occurred at the link #Gbetween the node #8 and the node #7. Due to a fault in link #G, the OAMpacket processor 64 in the receiving node #1 does not receive an OAMpacket of CCM transmitted by the OAM packet processor 64 in the node #6defining the terminal point of the working LSP-D. Accordingly, LOC ofthe working LSP-D is detected.

Next, as indicated in FIG. 29, the OAM packet processor 64 in thereceiving node #1 transmits an OAM packet of a LOC occurrence report(LOC-F) to the OAM packet processor 64 in the node #6 in the backupLSP-D in the D direction.

The OAM packet processor 64 in the node #6 defining the terminal pointof the working LSP-D receives an OAM packet of LOC-F from the receivingnode #1 in the backup LSP-D in the D direction. Furthermore, asindicated in FIG. 30, the OAM packet processor 64 in the node #6transmits an OAM packet of a switch request (SW-RQ) onto the workingLSP-D in the D direction. Furthermore, the OAM packet processor 64 inthe node #6 changes the LSP to which signals are to be added from theworking LSP-D to the backup LSP-C, according to descriptions relevant tofault recovery of the working LSP in the D direction in the LSPmanagement information indicated in FIG. 23.

The OAM packet processor 64 in the middle node #7 in the working LSP-Dreceives the OAM packet of SW-RQ from the node #6 defining the terminalpoint of the working LSP-D in the D direction. Furthermore, as indicatedin FIG. 31, the OAM packet processor 64 relays an OAM packet of SW-RQonto the working LSP-D in the D direction, and changes the LSP to whichsignals are to be added from the working LSP-D to the backup LSP-C,according to descriptions relevant to fault recovery of the working LSPin the D direction in the LSP management information indicated in FIG.23. According to the above operations, signals added to the backup LSP-Cfrom the node #6 and the node #7 on the working LSP-D are connected tothe working LSP-C in the C direction at the node #4, and are transmittedto the receiving node #1 via the node #3 and the node #2, and the faultis recovered. That is to say, the transmission delay under normalcircumstances is reduced. Furthermore, at the time of fault recovery,the working LSP-C (nodes #4, #3, #2, #1) and the backup LSP-C (nodes #7,#6, #5, #4) in the C direction do not overlap each other, and thereforethe signal band is efficiently used.

The present embodiment is applicable to a working label switch path anda backup label switch path that are linked, and the network topology isnot limited to a ring.

According to an aspect of the present invention, the transmission delayis reduced.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

1. A ring network of a multicast label switch path scheme, the ringnetwork comprising: a transmitting node and a plurality of receivingnodes connected to form a ring, wherein a signal input to thetransmitting node is branched to be transmitted in first and seconddifferent directions to a first one and a second one of the receivingnodes through a first working path and a second working path,respectively, in the ring network, the first one and the second one ofthe receiving nodes defining terminal points of the first working pathand the second working path, respectively, from the transmitting node,and a first backup path is set from the first one of the receiving nodesto the transmitting node, and a second backup path is set from thesecond one of the receiving nodes to the transmitting node, wherein thefirst backup path is in an opposite direction to the first working pathand the second backup path is in an opposite direction to the secondworking path.
 2. The network according to claim 1, wherein thetransmitting node includes a controller configured to periodicallyinsert and transmit a first monitor/control packet in the first and thesecond working paths to monitor connections, and upon receiving a secondmonitor/control packet reporting a fault from the first or the secondbackup path, insert and transmit a third monitor/control packet in thefirst or the second working path, the third monitor/control packetinstructing the first one or the second one of the receiving nodesdefining the terminal point of the first or the second working path inan opposite direction to the first or the second backup path,respectively, to connect the first or the second working path to thefirst or the second backup path.
 3. The network according to claim 2,wherein the first one and the second one of the receiving nodes includea processor configured to, when no first monitor/control packet isreceived from the first and the second working paths, insert andtransmit the second monitor/control packet in the first and the secondbackup paths in the same direction as the first and the second workingpaths, respectively, and, upon receiving the third monitor/controlpacket from the first and the second working paths, connect the firstand the second working path to the first and the second backup path inthe same direction.
 4. The network according to claim 3, wherein each ofthe receiving nodes receives a signal from the first or the secondworking path and from the first or the second backup path.
 5. A faultrecovery method for backing up a ring network of a multicast labelswitch path scheme so that a signal input to a transmitting node isbranched to be transmitted in first and second different directionsthrough a first working path and a second working path to a first oneand a second one of receiving nodes, respectively, the fault recoverymethod comprising: setting the first and second working paths configuredto extend in the first and second different directions from thetransmitting node to the first one and the second one of the receivingnodes defining terminal points of the first working path and the secondworking path, respectively, the transmitting node and the first one andthe second one of the receiving nodes being included in the ringnetwork; setting first and second backup paths respectively set from thefirst one of the receiving nodes and the second one of the receivingnodes to the transmitting node, so that the first working path and thefirst backup path are connected to form a ring and the second workingpath and the second backup path are connected to form the ring, whereinthe first backup path is in an opposite direction to the first workingpath and the second backup path is in an opposite direction to thesecond working path; periodically inserting and transmitting, by thetransmitting node, a first monitor/control packet to monitor connectionsin the first and the second working paths; inserting and transmitting,by the first one or the second one of the receiving nodes defining theterminal point of one of the first and the second working paths thatdoes not receive the first monitor/control packet from the one of thefirst and the second working paths, a second monitor/control packetreporting a fault in one of the first and the second backup paths in thesame direction as the one of the first and the second working paths;inserting and transmitting, by the transmitting node, a thirdmonitor/control packet instructing to switch connection in another oneof the first and the second working paths that is in an oppositedirection to the one of the first and the second backup paths, when thesecond monitor/control packet is received from the one of the first andthe second backup paths; and connecting, by the first one or the secondone of the receiving nodes defining the terminal point of the other oneof the first and the second working paths, the other one of the firstand the second working paths with another one of the first and thesecond backup paths in the same direction as the other one of the firstand the second working paths, when the third monitor/control packet isreceived from the other one of the first and the second working paths.6. A ring network of a multiple-to-one connection label switch pathscheme, the ring network comprising: a receiving node and a plurality oftransmitting nodes connected to form a ring, wherein a signal input tothe receiving node is branched to be transmitted in first and seconddifferent directions to a first one and a second one of the transmittingnodes through a first working path and a second working path,respectively, in the ring network, the first one and the second one ofthe transmitting nodes defining terminal points of the first workingpath and the second working path, respectively, from the receiving node,and a first backup path is set from the first one of the transmittingnodes to the receiving node, and a second backup path is set from thesecond one of the transmitting nodes to the receiving node, wherein thefirst backup path is in an opposite direction to the first working pathand the second backup path is in an opposite direction to the secondworking path.
 7. The network according to claim 6, wherein the first oneand the second one of the transmitting nodes respectively defining theterminal points of the first working path and the second working pathinclude a processor configured to periodically insert and transmit afirst monitor/control packet in the first and the second working pathsto monitor connections, and upon receiving a second monitor/controlpacket reporting a fault from the first and the second backup paths inthe same direction as the first and the second working paths, insert andtransmit a third monitor/control packet instructing to switch connectionin the first and the second working paths in the same direction as thefirst and the second backup paths, and switch a path to which signalsare inserted from the first and the second working paths to the firstand the second backup paths in an opposite direction to the first andthe second working paths.
 8. The network according to claim 7, whereinthe receiving node includes a processor configured to, when no firstmonitor/control packet is received from the first and the second workingpaths, insert and transmit the second monitor/control packet in thefirst and the second backup paths in the same direction as the first andthe second working paths, respectively.
 9. The network according toclaim 8, wherein the transmitting nodes include a processor configuredto, upon receiving the third monitor/control packet from the first andthe second working paths, relay the third monitor/control packet andswitch a path to which signals are inserted from the first and thesecond working paths to the first and the second backup paths in anopposite direction to the first and the second working paths.
 10. Afault recovery method for backing up a ring network of a multiple-to-oneconnection label switch path scheme so that a signal input to areceiving node is branched to be transmitted in first and seconddifferent directions through a first working path and a second workingpath to a first one and a second one of transmitting nodes,respectively, the fault recovery method comprising: setting the firstand second working paths configured to extend in the first and seconddifferent directions from the receiving node to the first one and thesecond one of the transmitting nodes defining terminal points of thefirst working path and the second working path, respectively, thereceiving node and the first one and the second one of the transmittingnodes being included in the ring network; setting first and secondbackup paths respectively set from the first one of the transmittingnodes and the second one of the transmitting nodes to the receivingnode, so that the first working path and the first backup path areconnected to form a ring and the second working path and the secondbackup path are connected to form the ring, wherein the first backuppath is in an opposite direction to the first working path and thesecond backup path is in an opposite direction to the second workingpath; periodically inserting and transmitting, by the first one and thesecond one of the transmitting nodes respectively defining the terminalpoints of the first working path and the second working path, a firstmonitor/control packet in the first and the second working paths tomonitor connections; inserting and transmitting, by the receiving node,a second monitor/control packet in the first and the second backup pathsin the same direction as the first and the second working paths,respectively, when no first monitor/control packet is received from thefirst and the second working paths; inserting and transmitting, by thefirst one and the second one of the transmitting nodes respectivelydefining the terminal points of the first working path and the secondworking path, a third monitor/control packet instructing to switchconnection in the first and the second working paths in the samedirection as the first and the second backup paths, and switching a pathto which signals are inserted from the first and the second workingpaths to the first and the second backup paths in an opposite directionto the first and the second working paths, upon receiving the secondmonitor/control packet from the first and the second backup paths in thesame direction as the first and the second working paths; and relaying,by the transmitting node that has received the third monitor/controlpacket, the third monitor/control packet, and switching a path to whichsignals are inserted from the first and the second working paths to thefirst and the second backup paths in an opposite direction to the firstand the second working paths.